This article is from the CD-Recordable FAQ, by Andy McFadden (email@example.com) with numerous contributions by others.
A CD has a single spiral track, each revolution of which is separated by 1.6
microns on a 74-minute disc (less on higher-capacity discs). The mirrored
"grooves" act as a reflection diffraction grating, causing interference
patterns in the reflected light.
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